[photon-core] 2D Detection data accuracy

[amquake]

• Use calibration data for 2d target info when available (principal point, FOV)
• Correct perspective distortion in 2d yaw/pitch info
  • Explanation:

    The pitch traditionally calculated from pixel offsets do not correctly account for non-zero values of yaw because of perspective distortion (not to be confused with lens distortion)-- for example, the pitch angle is naively calculated as:

    pitch = arctan(pixel y offset / focal length y)

    However, using focal length as a side of the associated right triangle is not correct when the pixel x value is not 0, because the distance from this pixel (projected on the x-axis) to the camera lens increases. Projecting a line back out of the camera with these naive angles will not intersect the 3d point that was originally projected into this 2d pixel. Instead, this length should be:

    focal length y ⟶ (focal length y / cos(arctan(pixel x offset / focal length x)))

    This cannot, however, account for perspective distortion in the calculation of the target center (averaging the contour corners).
• Undistort detected target corners when calibration data is available?
  • We currently only do this for AprilTag detections when passing to pose estimation. Not sure how correct it would be for all targets or if it's even helpful. Relevant: Undistorting 2d detection results #643 Nah
• Verified on hardware

[amquake]

@mcm001 Thoughts on inverting 2d target yaw / pitch here to match wpilib?

[mcm001]

I'm not sure. I see arguments on both sides. If we yell very loudly that it changed, it'll be fine? Like it needs to be at the top of our release notes.

Or @Bankst should we leave it as is?

[mdurrani808]

I'm not sure. I see arguments on both sides. If we yell very loudly that it changed, it'll be fine? Like it needs to be at the top of our release notes.

Or @Bankst should we leave it as is?

I say we leave it as is and maintain parity with what LL has (large amount of users are coming from there or have experience with LL system anyways).